LilyPad ProtoSnap Plus Activity Guide

Contributors: MikeGrusin, Gella

7: Sensing Light

This activity will also use inputs, this time to sense ambient light in the room and use that reading to light up LEDs. The light sensor is an analog sensor which provides a range of values instead of the digital ON/OFF of the buttons and switches example.

LilyPad Boards Used in This Activity

• LilyPad USB Plus
• LilyPad Light Sensor
• Red LilyPad LEDs
• Green LilyPad LEDs
• Blue LilyPad LEDs

New Concepts Introduced in This Activity

Analog Input: Analog to Digital Conversion

In this activity, we’ll explore reading input from a sensor in a new way using analog input. Notice that certain sew tabs on the LilyPad USB Plus include an ‘A’ in front of the number - this indicates the pins on the controller and tabs that are connected have an Analog to Digital Converter (ADC). These pins can “sample” an analog signal being read by the controller and translate it to a digital signal that the controller can interpret.

In the last activity, we used digital inputs that read only two states. The LilyPad Light Sensor is an analog sensor, meaning it can read a wide range of values. For analog inputs, the values range from 0 (0V) to 1023 (3.3V).

Serial Monitor and Serial Commands

When using the button and switch, it was pretty easy to tie the ON/OFF to an LED turning ON/OFF. For sensors reading a range of values, it is more useful to actually see those numbers and make decisions using them. The Serial Monitor and Serial Commands are useful tools for displaying information from variables or other debugging tools for your code.

Example Code

To open the code, go to:

File > Examples > LilyPadProtoSnapPlus > LPP_07_Light

You can also copy and paste the following code into the Arduino IDE. Hit upload, and see what happens!

language:c
/*
LilyPad ProtoSnap Plus Activity 7: Sensing Light
SparkFun Electronics
https://www.sparkfun.com/products/14346

Explore analog input from the light sensor

Follow the tutorial at: 
https://learn.sparkfun.com/tutorials/lilypad-protosnap-plus-activity-guide#7-sensing-light

This code is released under the MIT License (http://opensource.org/licenses/MIT)

******************************************************************************/

// Create variables for the pins we'll use:

int sensorPin = A2;

int redLED = 6;
int greenLED = A7;
int blueLED = A8;

void setup()
{
  // Initialize the sensor pin as an input, but without a pullup
  // (Pullups are only used for switch inputs)

  pinMode(sensorPin, INPUT);

  // Initialize the output pins:

  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(blueLED, OUTPUT);

  // Initialize the serial monitor:

  Serial.begin(9600);
}

void loop()
{
  int sensorValue;

  // Read the sensor value (will be 0 to 1023):

  sensorValue = analogRead(sensorPin);

  // Print out the sensor reading to the serial monitor:

  Serial.print("sensor value: ");
  Serial.println(sensorValue);

  // Since the sensor value is 0 to 1023,
  // and analogWrite needs a value from 0 to 255,
  // we'll divide the sensor value by four to scale it down:

  analogWrite(redLED,sensorValue / 4);
  analogWrite(greenLED,sensorValue / 4);
  analogWrite(blueLED,sensorValue / 4);
}

What You Should See

Hold your hand over the light sensor to change the amount of light it is exposed to and observe the red, green, and blue LilyPad LEDs. As the light sensor reads less light, the LEDs will reflect the light levels with their brightness levels. You can also use a flashlight to shine more light on the sensor and observe how it affects the LEDs.

Understanding Your Program

Program Overview

1. Store the light level in the variable sensorValue.
2. Print the reading to the Serial Monitor.
3. Set the brightness level of the red, green, and blue LEDs to the number stored in the sensorValue variable divided by 4.
4. Repeat.

Code to Note

Coding Challenges

• Can you change the code so that the built-in RGB LED displays a brighter or dimmer white when the light levels change?

• Can you change the code so that two colors mix on the RGB LED when the light levels change?

• Can you create a blink pattern where the speed of the blink is determined by the light sensor readings?